EXCHANGE 


Manganese 

in 
The  Catalytic  Oxidation  of  Ammonia 


DISSERTATION 


iUBMlTTED  TO  THE  BOARD  OF  UNIVERSITY  STUDIES  OF 
THE  JOHNS  HOPKINS  UNIVERSITY  IN  CONFORMITY 
WITH  THE  REQUIREMENTS  FOR  THE  DEGREE 
OF  DOCTOR  OF  PHILOSOPHY 


BY 

CHARLES  SNOWDEN  PIGGOT 
June,  1920 


EASTON,  PA.: 
ESCHENBACH  PRINTING  Co. 

1922 


Manganese 

in 
The  Catalytic  Oxidation  of  Ammonia 


DISSERTATION 


SUBMITTED  TO  THE  BOARD  OF  UNIVERSITY  STUDIES  OF 

THE  JOHNS  HOPKINS  UNIVERSITY  IN  CONFORMITY 

WITH  THE  REQUIREMENTS  FOR  THE  DEGREE 

OF  DOCTOR  OF  PHILOSOPHY 


BY 

CHARLES  SNOWDEN  PIGGOT 

June,  1920 


EASTON,  PA.: 
ESCHENBACH  PRINTING  Co. 

1922 


TABLE  OF  CONTENTS. 

Acknowledgment 4 

Introduction 5 

I  Oxide  Catalysts 6 

II  Manganese  Alloys 8 

Apparatus 10 

Summary 16 

Biography 18 


543936 


ACKNOWLEDGMENT. 

The  author  wishes  to  express  his  appreciation  and  gratitude  for  the  in- 
terest and  helpful  advice  of  Professor  J.  C.  W.  Frazer  under  whose  direc- 
tion this  work  was  carried  out.  He  wishes  also  to  thank  President  Ira 
Remsen,  Professor  E.  E.  Reid,  Associate  Professors  W.  A.  Patrick  and 
B.  F.  Lovelace,  and  Collegiate  Professor  C.  K.  Swartz  for  advice  and 
inspiration  received  in  the  laboratory  and  lecture  room.  Thanks  are 
also  here  expressed  to  Dr.  C.  H.  Milligan  for  assistance  cheerfully  given 
on  many  occasions. 


MANGANESE  IN  THE  CATALYTIC  OXIDATION  OF  AMMONIA. 


Introduction. 

In  the  course  of  certain  investigations  undertaken  in  this  laboratory 
during  the  war  seeking  to  afford  protection  to  those  exposed  to  the  danger 
of  inhaling  carbon  monoxide,  a  number  of  oxide  catalysts  were  produced 
some  of  which  were  very  active  oxygen  carriers  and  served  to  completely 
give  the  protection  sought. 

The  synthesis  of  ammonia  having  been  accomplished,  the  production 
of  nitric  acid  therefrom  has  come  to  be  one  of  the  important  sources  of 
this  acid.  The  oxidation  of  ammonia  to  nitric  acid  is  always  accom- 
plished by  catalytic  oxidation,  using  air  and  some  form  of  platinum  as 
the  catalyst.  The  prospective  scarcity  of  platinum  made  it  desirable  to 
find  a  cheaper  catalyst,  and  the  possibility  of  substituting  some  of  the 
oxide  catalysts  already  in  hand  for  this  reaction  was  a  problem  of  con- 
siderable interest  at  the  time.  The  work  was  begun  shortly  before  the 
close  of  hostilities  and  has  been  continued  since  for  the  purpose  of  securing 
sufficient  data  to  give  a  comparison  between  these  oxide  type  of  catalysts 
and  platinum  for  the  oxidation  of  ammonia.  It  was  thought  that  possibly 
these  oxide  catalysts  would  be  less  influenced  by  the  "poisonous"  action 
of  certain  substances  which  in  the  case  of  platinum  seriously  interfere 
with  the  reaction  and  necessitate  the  removal  of  the  platinum  gauzes  at 
certain  intervals.  At  least  it  was  thought  that  should  these  oxide  cata- 
lysts show  an  efficiency  at  all  comparable  with  that  of  platinum  their 
cheapness  would  make  their  renewal  a  much  less  serious  matter. 

It  has  been  shown  that  the  oxidation  of  the  ammonia  is  only  one  step 
of  the  reaction  involved,  there  being  the  possibility  that  the  first  products 
of  the  reaction  may  decompose  to  oxygen  and  nitrogen  in  the  presence 
of  the  catalyst  and  thus  greatly  lower  the  total  efficiency  of  the  reaction. 
It  was  anticipated  that,  inasmuch  as  the  catalytic  decomposition  of  the 
first  products  of  the  reaction  depends  largely  on  the  structure  of  the  cata- 
lyst, the  oxide  catalysts  as  first  prepared  would  not  be  suitable  for  the 
reaction.  This  view  was  subsequently  partially  confirmed.  At  the  same 
time,  however,  it  was  thought  that  the  increased  activity  of  these  mixed 
oxides  as  oxygen  carriers  over  that  of  the  single  constituents  of  such 
mixtures  could  be  retained  by  making  alloys  of  the  metals  in  question 


6 

and  then  subjecting  these  to  superficial  surface  oxidation  in  order  to  obtain 
the  proper  condition  for  their  use.  For  this  reason  most  of  the  results 
here  recorded  have  been  obtained  by  the  use  of  alloys. 

Manganese  alloys  were  investigated  because  it  was  found  that  man- 
ganese dioxide  was  an  essential  constituent  of  all  the  successful  oxide 
catalysts  previously  investigated  and  because  the  chemical  nature  of 
manganese  made  it  a  promising  substance  with  which  to  compound  a 
poly  component  catalyst. 

The  investigation  is  divided  into  two  parts ;  first,  the  study  of  the  oxide 
catalysts;  and  second,  the  study  of  manganese  alloys. 

Oxide  Catalysts. 

Manganese  Dioxide. — Ordinary  manganese  dioxide  was  found  to 
have  little  catalytic  effect  on  the  oxidation  of  ammonia,  but  when  in  a  state 
of  fine  sub -division  it  acted  as  a  catalyst  for  this  reaction. 

It  was  prepared  by  adding  powdered  potassium  permanganate  to  cold 
cone,  sulfuric  acid  and  allowing  the  permanganic  acid  thus  formed  to 
decompose  spontaneously  into  manganese  dioxide  and  oxygen.1  It 
was  then  washed  by  decantation  until  free  from  sulfates,  filtered  and  par- 
tially dried  on  a  water-bath.  When  the  water  content  had  been  reduced 
to  about  50%  it  was  subjected  to  a  pressure  of  2818  kg.  per  sq.  cm.  for  24 
hours.  The  resulting  cake  was  broken  up  and  completely  dried  in  a  stream 
of  oxygen  at  130-140°.  When  tested2  on  ammonia  this  material  showed 
considerable  catalytic  effect,  as  is  shown  in  Table  I  following. 

TABLE  I. — MANGANESE  DIOXIDE. 

Temp,  of  catalyst  =  800°.    NH8,  300  cc./min. 

Time  of  contact  =  0.05  sec.     Air,  3200  cc./min. 

Time  of  run  50  minutes.     1.0  cm.  layer. 

In.  HNO«  Eff.  Remarks. 

g-  %. 

Out. 

37.74  23.88  63.27  not  pressed 

37.86  24.19  63.90  not  pressed 

37.74  23.72  62.85  not  pressed 

38.23  36.52  95.44  pressed 

38.63  30.64  79.31  pressed 

38.85  29.46  75.84  pressed 

Though  functioning  catalytically  the  oxide  undergoes  some  change 
during  the  reaction.  The  color  changes  from  black  to  a  light  yellowish- 
brown,  the  material  having  changed  apparently  from  the  dioxide  to  a 
lower  oxide  of  manganese. 

1  Fremy,  Compt.  rend.,  82,  1231  (1876). 

2  The  difficulties  associated  with  the  quantitative  estimation  of  oxidized  nitrogen 
as  described  later  in  this  article  applied  equally  here. 


Mixture  of  Oxides. — Precipitated  manganese  dioxide  when  mixed 
with  various  proportions  of  silver  oxide  or  copper  oxide  or  with  both  of  these 
oxides  produces  a  catalyst  which  is  quite  active  in  the  oxidation  of  ammonia. 

The  manganese  dioxide  used  for  these  mixtures  was  prepared  by  treating 
a  concentrated  solution  of  potassium  permanganate  at  80°  with  methyl 
alcohol,  filtering  on  a  Buchner  funnel,  washing  and  drying  to  about  50% 
water  content,  this  latter  being  determined  by  analysis.  A  weighed 
quantity  of  this  paste  was  made  into  a  fine  suspension  in  water  and  the 
proper  amount  of  silver  added  in  the  form  of  silver  nitrate  solution.  Silver 
oxide  was  then  precipitated  on  the  manganese  dioxide  by  means  of  a  slight 
excess  of  strong  sodium  hydroxide  solution.  The  two  oxides  quickly  settle 
out  as  a  single  precipitate.  When  silver  and  copper  were  used  together 
they  were  added  in  the  form  of  their  nitrate  solutions  as  above.  When 
copper  alone  was  added  it  was  usually  added  as  the  sulfate  and  precipitated 
by  sodium  carbonate.  In  any  case  the  precipitates  were  washed  by  de- 
cantation  until  free  from  alkali  or  sulfates,  filtered  with  suction  and  dried 
in  a  current  of  oxygen  at  130-140°.  The  dry  cake  was  broken  up,  screened 
to  convenient  size  and  used  for  testing. 

Catalysts  so  made  have  proved  to  have  considerable  activity,  are  very 
porous,  thus  offering  a  very  large  surface,  and  are  quite  resistant  to  the 
high  temperatures  of  the  reaction,  i.  e.,  they  show  no  tendency  to  sinter 
together  even  when  the  temperature  is  raised  to  1000°  or  more.  The 
activity  can  be  more  or  less  closely  controlled  by  the  method  of  preparing 
the  catalytic  mixture;  mixtures  containing  the  constituents  in  a  very 
fine  state  of  subdivision  and  in  intimate  contact  being  much  more  active 
than  those  in  which  the  reverse  is  true. 

The  disadvantages  of  such  catalysts  are  softness,  tendency  to  crumble 
and  produce  fines  which  clog  the  gas  passages,  their  tendency  to  take 
up  moisture  due  to  their  extreme  porosity,  the  fact  that  in  contact 
with  a  liquid  they  disintegrate,  and  that  liquid  nitric  acid  will  dissolve 
out  the  silver  or  copper  oxides.  Tables  II,  III  and  IV  show  the  results 
of  the  tests  on  these  oxide  mixtures. 

Manganese  dioxide  when  prepared  by  the  Fremy  method  and  mixed 
with  silver  oxide,  copper  oxide,  or  mixtures  of  both,  produces  materials 
which  are  such  vigorous  oxidizing  catalysts  that  the  ammonia  is  largely 
converted  into  nitrogen  and  water,  with  a  consequent  low  efficiency  for 
nitric  acid. 

TABLE  II. — MIXTURES  OF  OXIDES. 

Composition:    MnO2  (Fremy),  71.43%;  CuO,  21.43%;  Ag2O,  7.14%;  dried  at  135°. 
Time  of  contact,  0.11  sec.     NH8,  300  cc./min.     Air,  3200  cc./min.     Temp,  of  cat.. 
800°.     Time  of  run,  50  min.     1.8  cm.  layer. 

HNO«  Efficiency 

In.  g.     Out.  %. 

38.63  18.85  48.77 

38.77  21.10  54.41 


Manganese  dioxide  prepared  by  treating  hot  (100°  approx.)  potassium 
permanganate  solution  with  methyl  alcohol  is  relatively  coarse  in  structure 
and  consequently  not  so  active.  This  type  was  used  in  preparing  mix- 
tures of  which  the  following  is  a  fair  example.  Though  not  so  active  an 
oxidizing  catalyst  it  gave  greater  efficiencies  based  on  the  nitric  acid  yield. 

TABLE  III. — MIXTURES  OF  OXIDES  CONTAINING  COARSER  MANGANESE  DIOXIDE. 
Composition:    MnO2,  60%;    CuO,  40%;    dried  at  140°.    4  cm.  layer.     Time  of  con- 
tact, 0.2  sec.     NH3,  300  cc./min.    Air,  3500  cc./min.     Temp,  of  cat.,  800°.      Copper 

precipitated   as  carbonate. 

HNOt  Eff. 

In.  g.  Out.  %. 

38.10  33.80  88.96 

38.60  37.74  97.71 

38.62  33.79  87.50 

38.62  38.29  96.57 

38.23  36.69  95.98 

Manganese  dioxide  was  prepared  as  for  the  MnO2-CuO  mixture  de- 
scribed above  and  mixed  with  silver  oxide,  the  latter  being  precipitated 
on  the  former  from  the  nitrate  solution  by  sodium  hydroxide.  The 
efficiency,  not  high  at  first,  rapidly  decreased.  The  time  of  exposure  of 
each  charge  was  6  hours. 

TABLE  IV. — OXIDES  OF  MANGANESE  AND  SILVER. 
Composition:  MnO2,62.5%;  Ag2O,  37.50%.      1  cm.  layer. 


Time  of 
contact. 

NHs 
cc./min. 

Air 
cc./min. 

HNO». 
In.                    Out. 

Temp, 
cat. 

Eff. 

Sec. 

G.                                 °C. 

0.082 

400 

4200 

50.67 

29.37 

650 

57.9 

0.082 

400 

4200 

50.67 

29.86 

650 

58.8 

0.082 

400 

4200 

51.36 

37.42 

790 

72.86 

0.082 

400 

4200 

51.50 

34.65 

820 

67.20 

0.057 

300 

3000 

38.52 

24.69 

800 

64.11  NH3  pass- 

New Charge 

2  cm.  layer. 

ing 

0.13 

200 

2600 

25.49 

21.55 

700 

84.52 

0.13 

200 

2600 

25.42 

20.04 

700 

81.04 

0.13 

200 

2600 

25.42 

20.60 

800 

79.00 

0.13 

200 

2600 

25.42 

19.34 

800 

76.  09  NH3  pass- 

ing 

0.057 

300 

3100 

38.23 

22.62 

800 

57.16      " 

II.    Manganese  Alloys. 

The  variable  valence  of  manganese  together  with  its  other  chemical 
properties,  recommended  it  as  a  good  catalytic  agent  if  brought  into  in- 
timate contact  with  suitable  promoters.  It  was  thought  that  this  in- 
timate contact  might  well  be  obtained  in  an  alloy.  The  advantages 
of  an  easily  workable  metallic  catalyst  are  many ;  as  for  instance  the  possi- 
bility of  making  connections  and  reaction  chambers  of  it  and  the  weaving 
of  gauzes  for  the  actual  contact  material. 


9 

S.  F.  Zhemchuzhnii  and  V.  K.  Petrashevich8  state  that  they  have  been 
able  to  cold  draw  a  manganese  alloy  of  the  composition  1.1%  Fe,  3. 53%- 
Cu,  0.50%  Al,  0.12%  Si  and  94.75%  Mn,  to  a  wire  1  to  1.5mm.  diameter 
without  annealing  between  passes.  None  of  the  alloys  used  in  this  in- 
vestigation, though  more  or  less  ductile,  exhibited  such  ductility  as  indi- 
cated by  the  above. 

Some  6  months  of  the  investigation  were  devoted  to  the  problem  of 
obtaining  a  manganese  alloy  relatively  free  from  impurities  (Fe,  C,  Si). 
This  proved  very  difficult,  and  has  not  been  entirely  solved  up  to  the  pres- 
ent time. 

Crucibles  of  carbon,  silicon,  or  porcelain  were  of  course  out  of  the  question,  and  the 
usual  magnesite  crucibles  proved  to  be  too  porous  and  frail  for  melting  satisfactorily 
200-  to  400-g.  charges  of  material. 

Alundum  crucibles  tended  to  adsorb  large  quantities  of  the  molten  manganese, 
forming  a  slag  coating  which  was  extremely  hard.  This  difficulty  was  only  partially 
overcome  by  lining  the  crucibles  with  magnesium  oxychloride.  The  most  satisfactory 
crucibles  so  far  tried  were  made  from  a  magnesite — iron  oxide  mixture  of  about  the 
same  composition  as  that  used  in  making  the  ordinary  magnesite  brick  for  iron  smelting 
purposes. 

When  using  a  molybdenum- wound  "hydrogen"  furnace,  the  hydrogen  formed 
many  "blow  holes"  in  the  ingots,  the  small  magnesite  crucibles  being  too  frail  to  permit 
pouring. 

With  an  electric-resistance  vacuum  furnace  the  volatilization  of  the  manganese 
was  excessive  even  when  the  furnace  was  filled  with  hydrogen  under  slightly  reduced 
pressure. 

The  best  results  have  been  obtained  by  using  the  magnesium  oxide — iron  oxide 
crucible  as  stated  above,  and  a  Seger  gas  furnace.  The  melt  was  covered  with  fused 
sodium  borate  as  a  flux,  and  the  charge  was  protected  as  much  as  possible  from  contact 
with  the  furnace  gases  by  enclosing  the  crucible  in  a  fire-clay  muffle.  The  best  ob- 
tainable thermit-process  manganese,  and  electrolytic  copper  and  silver  were  used. 
A  comparatively  large  charge  was  melted  and  the  best  of  the  metal  poured  into  a  steel 
mould  coated  with  graphite,  giving  a  rod  12  mm.  in  diameter  by  15cm.  long,  which 
required  about  half  the  metal  of  the  melt.  This  rod  was  then  turned  on  a  lathe  and 
the  turnings  after  oxidizing  were  used  as  catalysts. 

Considerable  time  was  devoted  to  various  methods  of  oxidizing  me- 
tallic surfaces  so  as  to  give  a  firm  and  adherent  coating  as  well  as  one  of 
maximum  activity.  Various  gauzes,  especially  those  containing  manga- 
nese were  investigated  with  this  end  in  view,  the  final  result  being  the 
method  of  electrolytic  oxidation  described  below. 

The  preliminary  oxidation  of  the  catalysts  was  done  electrolytically, 
the  turnings  being  placed  in  a  porous  cup  and  made  the  anode  by  thrusting 
a  platinum  wire  into  the  mass.  The  electrolyte  used  was  0. 1  N  sodium 
hydroxide  solution.  A  current  of  0. 5  to  1 . 0  ampere  was  passed  for  from 
3  to  4  hours,  the  potential  across  the  electrodes  being  10. 0  to  15. 0  volts. 

This  treatment  caused  the  material  to  be  thoroughly  oxidized  super- 

6  Zhemchuzhnii  and  Petrashevich,  Bull.  acad.  sci.,  1917,  863-76. 


10 

ficially,  with  a  very  adherent  dark  brown  coating.     After  being  washed  and 
dried  it  was  ready  for  testing. 

It  was  found  in  the  course  of  the  investigation  that  it  was  not  essential 
to  oxidize  the  alloys  before  using,  for  like  the  platinum  gauzes  they  could 
be  "activated"  by  exposure  at  600—700°  to  the  ammonia-air  mixture,  for 
several  hours.  However,  the  electrolytic  method  was  more  rapid  and 
satisfactory,  and  was  the  usual  method  employed. 

Analytical  Difficulties. 

A  very  troublesome  problem  was  the  devising  of  a  suitable  testing  and  analytical 
method,  and  the  building  of  a  satisfactory  apparatus  to  put  the  same  into  operation. 
The  chief  difficulty  was  to  prevent  as  much  as  possible  the  decomposition  of  the  nitric 
oxide  once  formed  and  to  bring  about  its  complete  oxidation  to  nitrogen  dioxide  or  the 
higher  oxides  and  to  insure  their  absorption.  This  was  accomplished  by  using  oxida- 
tion towers  of  large  volume,  water  vapor  in  the  form  of  saturated  steam,  and  vigorous 
agitation  by  means  of  high-speed  stirring. 

Nitrogen  oxides  are  very  difficult  to  absorb,  as  is  also  ammonium  nitrate,  the  latter 
especially  so  when  in  the  condition  of  a  colloidal  "smoke."  Efforts  were  first  directed 
toward  absorbing  the  oxides  of  nitrogen  in  towers  of  various  types.  Soda-lime,  sodium 
hydroxide,  water,  hydrogen  peroxide,  potassium  permanganate  solution,  cone,  sulfuric 
acid,  etc.,  were  tried  separately  and  in  conjunction. 

The  efficiency  was  to  be  calculated  on  the  basis  of  the  oxygen  used  up.  This  in- 
volved accurate  measurement  of  flows  of  affluent  and  effluent  gases  and  absolute  oxi- 
dation and  absorption  of  the  nitrogen  oxides.  All  such  methods  proved  unavailing. 
Various  types  of  flow-meters  were  made  and  tried  but  none  could  be  devised  which 
would  measure  accurately  the  varying  concentrations  of  the  various  oxides  of  nitrogen 
which  passed  through  it,  without  being  affected  thereby. 

Cone,  sulfuric  acid  may  absorb  oxides  of  nitrogen  quantitatively,  as  stated  by 
Nernst,  in  small  quantities  and  on  long  exposure;  but  it  was  found  entirely  inadequate 
under  the  conditions  of  this  investigation. 

Apparatus. 

The  apparatus  used  in  the  investigation  is  shown  diagrammatically  in  the  ac- 
companying drawing.  A,  A  are  two  10-liter  aspirating  bottles  which  serve  to  give 
volume,  and  allow  time  for  the.  oxidation  of  nitric  oxide  to  nitrogen  dioxide  or  the 
higher  oxides.  A  jet  of  low-pressure  steam  is  passed  in  at  S  which  furnishes  water 
for  the  formation  of  nitric  acid  which  is  drawn  off  at  N.  B  is  a  Hoskins  electric  furnace 
and  C  the  catalyst,  supported  on  a  Witt  plate,  the  whole  being  surrounded  by  an  auxili- 
ary heating  unit  which  serves  to  start  the  reaction  and  to  maintain  it  at  the  proper 
temperature.  The  clay  combustion  tube  which  contains  the  catalyst  passes  through 
the  two  heating  units  and  is  provided  in  one  side  with  a  porcelain  tube  through  which 
the  mixed  gases  enter.  It  is  connected  below  with  a  water-cooled  condenser  D  which 
serves  to  cool  the  products  of  the  reaction  quickly.  Tlje  catalyst  bed  is  provided  with 
a  small  quartz  bulb  in  which  is  a  thermocouple  whose  wires  lead  to  a  Leeds  and  North- 
rup  compensating  potentiometer.  £  is  a  coil  condenser,  which  serves  as  a  preheater 
of  the  mixed  gases,  through  the  jacket  of  which  steam  is  passed  at  from  140  to  210  g. 
per  sq.  cm.  pressure.  P  is  a  mixing  chamber  for  the  ammonia  and  air,  while  T'NHi 
Fa\T  are  flow-meters  for  the  measurement  of  these  gases  respectively.  G  is  the  ab- 
sorption apparatus  consisting  of  two  battery  jars  with  cold  water  circulating  in  the 
annular  space  between.  The  inner  jar  contains  sodium  hydroxide  solution  which  is 


11 

kept  stirred  by  the  stirring  mechanism  H  which  revolves  at  a  speed  of  10,000-20,000 
r.  p.  m.,  the  stirring  head  K  being  heavily  gold  plated.  This  stirring  head  is  so  con- 
structed that  the  entering  gases  and  vapors  are  sucked  up  at  the  center  and  thrown  out 
through  the  radial  holes,  which  at  the  speed  of  operation  brings  about  an  emulsoid 
condition  which  insures  a  very  thorough  mixing  and  accomplishes  complete  absorption 
of  the  vapors  of  nitric  acid  and  the  oxides  of  nitrogen.  Baffle  plates  are  provided  to 
prevent  a  circular  motion  of  the  liquid  and  to  prevent  the  latter  from  being  thrown 
out  of  the  container.  It  was  found  necessary  to  cool  the  solution,  as  otherwise  the 
heat  produced  by  the  rapid  stirring  during  a  run  was  sufficient  to  bring  the  solution 
almost  to  its  boiling  temperature.  The  water  (usually  slightly  acid)  produced  by  the 
oxidation  of  the  ammonia  is  collected  and  drawn  off  at  M.  If  desired,  an  auxiliary 
stream  of  air  could  be  passed  in  at  0,  but  this  was  seldom  used. 


The  flow-meters  were  carefully  calibrated  at  average  room  temperature,  25°, 
and  were  used  only  on  the  gas  with  which  they  had  been  previously  calibrated. 

Methods  of  Testing. 

In  making  a  run  the  following  procedure  was  usually  adopted.  1000 
cc.  of  N  sodium  hydroxide  solution  was  placed  in  the  adsorption  appa- 
ratus G\  and  the  catalyst,  placed  at  C,  heated  externally  to  about  600°. 
The  furnace  B  was  heated  to  its  maximum  temperature  (950-1000°) 
and  steam  passed  in  at  5  and  through  E.  Ammonia  from  a  steel  cylinder, 
and  air,  measured  by  their  respective  flow-meters,  were  passed  into  the 
mixing  chamber  P.  The  quantityof  air  mixed  with  the  ammonia  at 
this  point  was  usually  only  sufficient  to  furnish  a  volume  of  oxygen  equal 


12 

to  that  of  the  ammonia;  the  remaining  air  for  the  completion  of  the  re- 
action being  passed  through  the  other  air  flow-meter  and  down  through 
the  hot  furnace  B,  meeting  the  ammonia-air  mixture  just  before  contact 
with  the  catalyst.  This  air  was  heated  by  the  furnace  B  to  about  300° 
to  400°,  while  the  mixture  passing  through  the  preheater  E  was  heated  not 
above  90-100°,  thus  ensuring  no  decomposition  of  the  ammonia.  The 
liquids  which  collect  at  M  and  N  were  drawn  off  from  time  to  time  and 
added  to  the  sodium  hydroxide  solution  at  the  end  of  the  run.  At  first 
runs  of  100  minutes  were  made,  but  later  50-minute  runs  were  used  and  this 
time  was  maintained  throughout  the  remainder  of  the  investigation. 

The  gases  issuing  from  the  second  reaction  chamber  were  by-passed 
and  allowed  to  escape  for  some  time  until  the  run  became  stabilized  and 
everything  was  working  properly  before  a  test  was  begun. 

The  ammonia  entering  the  apparatus  was  calculated  as  g.  of  nitric  acid, 
HNO3,  due  correction  being  made  for  temperature  at  the  flow-meter! 
At  the  end  of  the  run  the  solution  in  G  was  measured  and  its  normality 
determined  by  titrating  a  10.  OOcc.  sample  with  N  hydrochloric  acid  using 
phenolphthalein  as  indicator.  From  this  the  g.  of  nitric  acid  pro- 
duced was  obtained  and  the  percentage  efficiency  calculated. 

To  the  10. OOcc.  sample  of  solution  from  G,  taken  above,  when  just 
neutralized,  was  added  an  additional  10.00  cc.  of  N  sodium  hydroxide 
solution,  any  ammonia  thus  liberated  was  boiled  off  and  the  solution  back 
titrated  with  N  hydrochloric  acid.  In  this  way  the  quantity  of  ammonia 
which  passed  the  catalyst  unoxidized  was  determined  and  could  be  cor- 
rected for.  This  procedure  however  was  not  always  necessary  as  even 
a  slight  trace  of  ammonia  passing  the  catalyst  would  fill  the  reaction 
chambers  with  a  dense  white  cloud  of  ammonium  nitrate  and  thus  indi- 
cate its  presence. 

A  number  of  preliminary  test  runs  were  made  to  determine  the  effect 
of  glass,  quartz,  porcelain,  and  other  materials  on  the  decomposition 
of  ammonia  and  the  oxides  of  nitrogen  when  formed.  All  those  materials 

Rate  of  NH3,  80  cc./min. 

Temp,  of  cat.  Eff. 

0  C.  Material.  %. 

900  Quartz                               33.40 

830  34.10 

800  40.48 

650  Pyrex                                 39.91 

630  35.50 

700  44.10 

800  59.10 

845  Clay                                   70.70 

850  75.60 

900  73.60 


13 

were  found  to  favor  the  decomposition  to  a  greater  or  less  extent,  quartz 
being  the  most  active  catalyst  for  this  decomposition. 

A  clay  combustion  tube  was  found  to  give  the  least  decomposition. 
Condensed  results  of  this  investigation  are  shown  briefly  in  the  following 
tabulation.  The  same  catalyst  was  used  throughout. 

After  the  clay  tube  was  adopted  an  idea  of  the  effect  of  heat  and  time 
of  heating,  on  the  decomposition  of  ammonia,  was  obtained  by  locating 
the  catalyst  bed  at  various  points  up  and  down  in  the  electric  furnace. 

Rate  of  NH3,  80  cc./min. 

Temp,  of  cat.  Eff. 

0  C.  %  Position  of  catalyst  bed. 

830  51.91  5  cm.  from  lower  end 

835  57.52  7.5  cm. 

845  70.70  Center  of  furnace 

850  68.62 

900  77  .  50  5  cm.  from  upper  end 

750  74.10 

850.  81.12 

These  results  led  to  the  adoption  of  the  arrangement  shown  in  the  drawing 
of  the  apparatus,  whereby  all  the  ammonia  and  about  }&  of  the  air,  after 
being  warmed  to  about  80°  enter  the  reaction  tube  just  above  the  cata- 
lyst bed  and  are  quickly  swept  down  over  the  latter  by  the  remaining  air 
which,  having  passed  through  the  furnace,  was  heated  to  about  300°. 

When  a  very  reactive  catalyst  was  being  tested  no  heat  at  all  was  neces- 
sary in  the  larger  furnace  ;  in  fact  it  was  sometimes  necessary  to  take  pre- 
cautions to  prevent  the  catalyst  from  melting. 

Experimental. 

As  has  been  indicated,  a  number  of  manganese  alloys  were  made.  The 
results  of  the  tests  of  those  which  were  examined  are  shown  in  the  tables 
below. 

TABLE  V. 
No.  1. 


Composition:   Mn,  48.78%;  Cu,  37.25%;   Ag,  12.70%;   Fe,  0.85%;   Sid,  0.50%. 

Run,  50  min.  0  .  5  cm.  layer.     Temp,  of  cat.,  800°. 

Time  of             NH3.  Air.                               HNOi.  Eff. 

contact.         Cc./min.  Cc./min.                In.                      Out.  %. 

Sec.  G. 

0.043            200  2000            25.58            15.88  62.08 

0.043            200  2000            25.58            16.06  62.60 

0.028,          300  3000            38.52            23.18  60.20 

0.028            300  3000            38.63            24.00  62.10 

0.028            300  3000            38.63            24.82  64.25 

0.022            400  4000            50.98            31.63  62.04 

0.022            400  4000            51.36            32.50  63.20 

An  alloy  containing  a  somewhat  higher  percentage  of  manganese  with 

consequent  lower  percentages  of  copper  and  silver  gave  better  yields  of 


14 


nitric  acid.     The  impurities  of  iron  and  silicon  were  also  higher, 
of  test  of  this  alloy  (No.  2)  are  shown  in  Table  VI. 


Results 


TABLE  VI. 

ALLOY  No.  2. 

Composition: 

Mn,  59. 

60%;    Cu,  27, 

,40%;    Ag,  8, 

55%; 

Fe,  3.25%; 

SiO2,  1.25%. 

Run,  50  min.     0.5  cm. 

layer. 

Time  of 

NH». 

Air. 

NHO» 

Temp. 

Eff. 

contact. 

Cc./min 

Cc./min. 

In. 

Out. 

of  cat. 

Sec. 

G. 

°  C. 

0.107 

80 

800 

10.48 

8.09 

838 

77.25 

0.107 

80 

800 

10.48 

8.38 

842 

79.95 

0.107 

80 

800 

10.13 

7.66 

848 

75.60 

0.045 

100 

2100 

12.92 

9.64 

800 

74.70 

0.045 

100 

2100 

12.84 

11.71 

800 

91.05 

0.045 

100 

2100 

12.79 

7.12 

800 

56.00 

0.045 

100 

2100 

12.84 

8.32 

800 

64.70 

0.051 

160 

1600 

20.88 

18.12 

856 

86.80 

0.043 

200 

2000 

25.68 

20.66 

800 

80.40 

0.043 

200 

2000 

26.01 

23.31 

855 

.     89.60 

0.043 

200 

2000 

26.01 

23.97 

857 

92.10 

0.022 

400 

4000 

52.03 

43.72 

800 

84.03 

0.022 

400 

4000 

51.88 

39.62 

800 

76.50 

0.022 

400 

4000 

52.02 

44.20 

800 

85.13 

0.022 

400 

4000 

51.88 

40.20 

800 

77.68 

0.022 

400 

4000 

51.50 

40.88 

800 

79.30 

0.022 

450 

4000 

51.40 

39.50 

800 

76.80 

0.019 

400 

4600 

58.15 

44.10 

800 

75.80 

0.019 

450 

4600 

57.90 

44.10 

800 

76.16 

0.019 

450 

4600 

57.76 

43.66 

800 

75.60 

0.017 

500 

5000 

64.37 

46.00 

800 

71.00 

0.017 

500 

5000 

61.60 

46.43 

800 

71.90 

An  alloy  high  in  manganese  was  made  and  tested  to  determine  the 
limiting  proportion  of  manganese.  This  alloy  was  not  analyzed  but  it  is 
believed  that  its  composition  closely  approximates  the  proportions  of  the 
constituents  which  were  weighed  into  the  melt:  i.  e.,  Mn,  80%;  Cu,  10%; 
Ag,  10%. 

TABLE  VII. 
ALLOY  No.  3. 

Composition:  Mn,  80%;  Cu,  10%;  Ag,  10%.     Run,  50  min.     0.5cm.  layer.      Temp. 

of  cat.,  800°. 


Time  of 

NH». 

Air. 

HNOi, 

Eff. 

contact. 

Cc./min. 

Cc./min. 

In. 

Out. 

%. 

Sec. 

G. 

0.032 

200 

2800 

25.58 

13.48 

52.85 

0.032 

200 

2800 

25.49 

13.45 

52.80 

0.027 

300 

3200 

38.23 

22.80 

59.65 

0.022 

400 

4800 

50.80 

23.56 

46.38 

It  is  evident  from  the  above  that  the  maximum  manganese  content 
lies  well  below  80%. 

Alloy  No.  4  of  the  following  composition:   Mn,  54.79%;   Cu,  43.77%; 


15 

Fe,  1.22%;  Si,  0 . 09%,- containing  no  silver  at  all,  showed  less  than  25% 
efficiency. 

Alloy  No.  5  was  made  with  the  idea  of  duplicating  No.  2.  Analysis 
showed  that  it  contained  Mn,  56.07%;  Cu,  32.81%;  Ag,  9.96%;  Fe, 
1.23%;  Si,  0.07%. 

TABLE  VIII. 
ALLOY  No.  5. 
Run,  50  min.    0 . 5  cm.  layer. 


Time  of 
contact. 
Sec. 

0.036 

NHj. 
Cc./min. 

200 

Air. 
Cc./min. 

2400 

HNOi. 
In.                    Out. 

25.58            14.91 

Temp, 
of  cat. 
°C. 

700 

Eff. 
%. 

58.27 

0.027 

300 

3200 

38.37            20.34 

700 

53.06 

0.027 

300 

3200 

38.62            18.67 

700 

48.34 

0.027 

300 

3200 

38.52            19.79 

800 

51.38 

0.027 

300 

3200 

38.37            18.27 

800 

47.60 

0.027 

300 

3200 

38.52            20.10 

800 

52.18 

0.027 

300 

3200 

38.52            20.85 

850 

54.13 

Discussion. 

As  stated  in  the  literature,  manganese  dioxide  was  found  to  have  some 
effect  as  a  catalyst  for  the  oxidation  of  ammonia. 

Early  in  this  investigation  it  was  shown  that  this  effect  can  be  greatly 
increased  by  the  method  of  preparing  the  oxide.  The  physical  structure 
of  the  material  is  of  great  importance,  extremely  fine  subdivision  giving 
a  large  adsorbing  surface  with  very  small  pores  being  conducive  to  greater 
activity. 

It  was  also  shown  that  suitable  promoters  have  a  great  influence  on 
the  catalytic  activity  of  the  material.  Manganese  dioxide  is  apparently 
reduced,  in  the  course  of  the  reaction,  to  some  lower  oxide  of  manganese, 
and  the  promoter  serves  to  aid  the  oxygen  to  reoxidize  it  back  to  the  di- 
oxide. This  is  indicated  by  the  fact  that  when  used  alone,  after  several 
hours,  the  greater  part  of  the  manganese  dioxide  is  reduced  to  the  lower 
reddish  colored  oxide.  That  part  of  the  material  which  remains  black 
(MnO2)  is  always  a  thin  layer  on  the  top  of  the  catalyst  bed,  being  that 
portion  which  first  comes  into  contact  with  the  air  and  is  consequently 
more  readily  re-oxidized.  When  a  promoter  is  mixed  with  the  manganese 
dioxide  very  little  of  the  material  shows  reduction  after  several  hours' 
use ;  in  this  case  the  reduced  area  (if  any)  is  always  at  the  bottom  of  the 
catalyst  bed  and  is  never  very  great. 

Manganese  dioxide  produced  by  the  action  of  methyl  alcohol  on 
potassium  permanganate  and,  consequently  consisting  of  comparatively 
coarse  particles,  was  always  less  completely  re-oxidized  by  the  promoter 
than  that  prepared  by  the  Fremy  method,  thus  indicating  qualitatively 
the  relation  of  subdivision  to  reactivity. 


16 

When  silver  and  copper  were  used  together  as  promoters  with  manganese 
dioxide  prepared  by  the  Fremy  method  (Table  II)  there  was  no  indication 
whatever  of  permanent  reduction  of  the  latter.  This  would  indicate  that 
these  two  materials  tend  to  act  as  very  efficient  carriers  of  oxygen  to  the 
manganese. 

On  the  other  hand,  however,  the  temperature  and  oxygen  pressure 
at  which  the  material  was  used  was  far  above  the  dissociation  temperature 
of  silver  oxide,  which  would  lead  to  the  conclusion  that  finely  divided 
silver  alone  is  as  effective  a  promoter  as  silver  oxide.  This  agrees  with  the 
conclusion  of  Lanning6  drawn  from  his  work  on  the  carbon  monoxide 
catalyst,  in  this  laboratory. 

The  low  yields  of  nitric  acid  obtained  from  the  3-component  mixtures 
as  shown  in  Table  II  coupled  with  the  fact  that  no  ammonia  was  detect- 
able in  tjie  effluent  gases  indicates  that  this  material  (the  catalyst  used  for 
carbon  monoxide  oxidation)  is  very  active  and  that  a  very  small  time  of 
contact  is  sufficient  for  it  also  to  favor  the  decomposition  of  the  nitric 
oxide  once  formed.  This  is  analogous  to  the  behavior  of  platinum  black 
when  used  alone  for  this  reaction.  -Some  mixture  should  be  possible 
which  would  be  just  active  enough  to  favor  the  formation  of  nitric  oxide 
while  preventing  the  liberation  of  elementary  nitrogen.  Such  a  mixture 
seems  to  be  approximated  by  that  shown  in  Table  III. 

It  was  shown  that  alloys  of  manganese  exist  which  possess  considerable 
catalytic  activity  for  this  reaction  and  the  data  point  toward  an  alloy 
of  rather  restricted  composition  which  gives  promise  of  high  efficiency. 
Such  an  alloy  should  exist  within  the  following  limits  of  composition: 
Mn,  55-65%;  Cu,  25-35%;  Ag,  5-15%;  Fe,  1-5%;  Si,  0-3%. 

Small  changes  of  composition  apparently  have  great  influence  on  the 
catalytic  activity  and  efficiency  and  it  is  believed  that  further  investi- 
gations in  this  more  restricted  field  will  develop  a  catalyst  which  will 
yield  an  efficiency  of  90  or  95%,  or  even  greater. 

Summary. 

Due  to  mechanical  difficulties  encountered  during  this  investigation 
the  above  experimental  data  are  not  as  extensive  or  complete  as  would  be 
desired.  It  is  believed,  however,  that  the  way  has  been  cleared  for  a  more 
comprehensive  and  exhaustive  study  of  this  subject  and  that  in  the  future, 
such  can  be  carried  out  without  great  difficulty. 

Mixtures  of  especially  prepared  manganese  dioxide  containing  promoters 
of  copper  and  silver  oxides  have  been  made  which  possess  great  catalytic 
activity  for  the  oxidation  of  ammonia  by  air. 

Attention  is  called  to  the  mixture  of  manganese  dioxide  and  cupric  oxide 
shown  in  Table  III.  This  mixture  apparently  possesses  as  great  efficiency 
6  Lanning,  Dissertation,  Johns  Hopkins  IJniv.,  June,  1920. 


17 

as  platinum  and  during  the  tests  showed  no  appreciable  deterioration  after 
6  hours  continuous  run. 

A  method  is  indicated  for  the  preparation  of  manganese  alloys  relatively 
free  from  impurities.  Alloys  of  manganese  with  silver  and  copper  have 
been  made  which  serve  as  catalysts  for  the  oxidation  of  ammonia,  and  the 
approximate  composition  of  an  alloy  is  indicated  which  should  give  a  high 
efficiency  for  this  reaction. 


BIOGRAPHY. 

Charles  Snowden  Piggot  was  born  in  1892  at  Swanee,  Tennessee. 
His  early  education  was  received  at  the  Swanee  Military  Academy  and  the 
Boy's  Latin  School  of  Baltimore,  Md.  He  entered  the  University  of  the 
South  in  1911,  graduating  with  the  degree  of  B.A.  in  1914.  The  school 
years  of  1914-15  and  1915-16  were  spent  in  post  graduate  work  in  Chem- 
istry at  the  University  of  Pennsylvania  where  he  held  the  University  and 
Harrison  Scholarships.  He  entered  Johns  Hopkins  University  in  1916 
taking  Chemistry,  Physical  Chemistry  and  Mineralogy  as  his  major  and 
subordinate  subjects  respectively.  The  years  1917-1918  were  spent  in 
the  United  States  Army  and  on  research  work  in  war  gases.  The  year 
1919-20  he  held  the  DuPont  Research  Fellowship  in  Chemistry. 


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